Window shades and blinds have been provided with various mechanisms to facilitate lifting. Among the roller shade mechanisms are the common spring loaded shade roller, shade rollers which are operated by chain wheels, inverted shades with rollers at the bottom, and shade rollers with internal motors. Blind mechanisms include the common venetian models and others mostly distinguished by the type of blind rather than the lifting method.
Of the above, only the common shade roller provides a means to balance the weight to be lifted and, even so, the shade must be overbalanced for proper operation of the mechanism. Furthermore, there is no arrangement to provide consistency in the balancing force versus the changing load of the shade as it is rolled up. This is apparent to anyone who has ever let go of a window shade without first setting the latching mechanism and has watched the shade abruptly snap upwards.
This invention uniquely provides a variable balancing force to track the changing load as a shade or blind is lifted. The mechanism is useful for shades, where the load decreases as the shade is lifted, and for blinds or inverted shades, where the load increases as the blind is lifted. The mechanism is also useful for other applications requiring constant balance of moving loads, particularly where space for the lifting mechanism is limited.